Regex

Regex - JS

.test() method takes the regex, applies it to a string (which is placed inside the parentheses), and returns true or false if your pattern finds something or not.

1. Match Literal Strings

let waldoIsHiding = "Somewhere Waldo is hiding in this text.";
let waldoRegex = /Waldo/; // Change this line
let result = waldoRegex.test(waldoIsHiding);

2. Match a Literal String with Different Possibilities

You can search for multiple patterns using the alternation or OR operator: |. Complete the regex petRegex to match the pets dog, cat, bird, or fish.

let petString = "James has a pet cat.";
let petRegex = /dog|cat|bird|fish/; // Change this line
let result = petRegex.test(petString);

3. Ignore Case While Matching

i flag /ignorecase/i

let myString = "freeCodeCamp";
let fccRegex = /freeCodeCamp/i;
let result = fccRegex.test(myString);

4. Extract Matches

So far, you have only been checking if a pattern exists or not within a string. You can also extract the actual matches you found with the .match() method.

let extractStr = "Extract the word 'coding' from this string.";
let codingRegex = /coding/;
let result = extractStr.match(codingRegex);

5. Find More Than the First Match

So far, you have only been able to extract or search a pattern once. To search or extract a pattern more than once, you can use the g flag.

let twinkleStar = "Twinkle, twinkle, little star";
let starRegex = /twinkle/ig; 
let result = twinkleStar;

6. Match Anything with Wildcard Period

Sometimes you won’t (or don’t need to) know the exact characters in your patterns. Thinking of all words that match, say, a misspelling would take a long time. Luckily, you can save time using the wildcard character: . For example, if you wanted to match hug, huh, hut, and hum, you can use the regex /hu./ to match all four words.

Complete the regex unRegex so that it matches the strings run, sun, fun, pun, nun, and bun. Your regex should use the wildcard character:

let exampleStr = "Let's have fun with regular expressions!";
let unRegex = /.un/;
let result = unRegex.test(exampleStr);

7. Match Single Character with Multiple Possibilities

For example, you want to match bag, big, and bug but not bog. You can create the regex /b[aiu]g/ to do this. The [aiu] is the character class that will only match the characters a, i, or u.

Use a character class with vowels (a, e, i, o, u) in your regex vowelRegex to find all the vowels in the string quoteSample.

let quoteSample = "Beware of bugs in the above code; I have only proved it correct, not tried it.";
let vowelRegex = /[aeiou]/gi;
let result = quoteSample.match(vowelRegex);
 

8. Match Letters of the Alphabet

For example, to match lowercase letters a through e you would use [a-e]. Match all the letters in the string quoteSample.

let quoteSample = "The quick brown fox jumps over the lazy dog.";
let alphabetRegex = /[a-z]/gi;
let result = quoteSample.match(alphabetRegex);

9. Match Numbers and Letters of the Alphabet /[0-5]/ matches any number between 0 and 5, including the 0 and 5. Also, it is possible to combine a range of letters and numbers in a single character set.

Create a single regex that matches a range of letters between h and s, and a range of numbers between 2 and 6. Remember to include the appropriate flags in the regex.

 
let quoteSample = "Blueberry 3.141592653s are delicious.";
let myRegex = /[h-s2-6]/gi;
let result = quoteSample.match(myRegex);

10. Match Single Characters Not Specified

you could also create a set of characters that you do not want to match. These types of character sets are called negated character sets. For example, /[^aeiou]/gi matches all characters that are not a vowel. Create a single regex that matches all characters that are not a number or a vowel. Remember to include the appropriate flags in the regex

let quoteSample = "3 blind mice.";
let myRegex = /[^aeiou0-9]/gi; // Change this line
let result = quoteSample.match(myRegex); // Change this line

11. Match Characters that Occur One or More Times

Sometimes, you need to match a character (or group of characters) that appears one or more times in a row. This means it occurs at least once, and may be repeated. You can use the + character to check if that is the case. Remember, * the character or pattern has to be present consecutively. That is, the character has to repeat one after the other For example, /a+/g would find one match in abc and return ["a"]. Because of the +, it would also find a single match in aabc and return ["aa"]. If it were instead checking the string abab, it would find two matches and return ["a", "a"] because the a characters are not in a row - there is a b between them. Finally, since there is no a in the string bcd, it wouldn’t find a match.

You want to find matches when the letter s occurs one or more times in Mississippi. Write a regex that uses the + sign.

let difficultSpelling = "Mississippi";
let myRegex = /s+/gi; // Change this line
let result = difficultSpelling.match(myRegex);

12. Match Characters that Occur Zero or More Times